Pump piping configuration 1

[devaxrayz]

Hi all,

I am in a work of sizing pump and its pipeline. The pump discharge has 2" nozzle and the pipe sizing is 6" diameter. Which should i use :

1) Either 2" block valve, 2" check valve and then expand the line to 6" diameter or,

2) expand the line to 6" diameter and use 6" block valve and 6" check valve.

Why?

Thanx for your help...

-Rayz-

 

[REFINERYPROJECTS]

Before answering your question, you need to look at you system (Piping arrangement and size, inlet pressure, discharge pressure, flow rate ... etc.) usually we expand the pipe gradually for example, from 2" to 4" to 6", to avoid pressure drop, you need to look at your complete piping system in order to size the pump correctly.

To start pump sizing, Pump are simply provided to overcome a systems natural resistance to flow. The first thing you need to do is determine the required flow, and then calculate the resistance in the system at that flow rate. There are many charts tables and programs to help you with this. Next you must select a pump that will fit the system

It is not enough to specify pumps based on anticipated head losses, you need also to measure the other losses.

The final check when selecting a pump is to make sure the net available suction head exceeds the required net suction head. This insures the application will not cause
vaporization inside the pump causing (cavitation).

 

[Artisi]

My first question is, if you are designing this system from scratch, why are you using 6" pipe on a 2" pump.

Naresuan University
Phitsanulok
Thailand

 

[pumpkind]

If indeed you are in no position to query why a 6 "
discharge piping is used on a 2 " pump - as rightly Artisi has pointed out - there is no economical uncertainty about the valve -> 2 " is vastly cheaper than 6 " valve and there is no engineering advantage to go for the bigger valve in this case either.

 

[EdStainless]

Just remember, the 2" valve and check will have a lot higher PD than a larger one. You may be better off playing this one down the middle, expand to 3" or 4" (some intermediate size) and put the valves there, then expand to your 6".

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[checman]

Devaxrayz I agree with refineryprojects more information is needed for a more complete answer. Saying that there are a few good points mentioned above. I am assuming that your 6” header is sized correctly you will want to make sure that it is under sufficient pressure to avoid the sudden pressure drop already mentioned above also you will want to check velocity head of the 2” line and make sure it will not disrupt flow in your 6” header. Turbulence created from the 2” lines velocity head can act as an obstruction in your 6” header. If you are not satisfied in either case stepping up to the 4” would be a good idea. That would add a new twist to your piping lay out, would you put the valves in the 2, 4 or 6” line. It would just make sense to use the smallest valves that would do the job trouble free. You will want to look at velocities (this is extra important if there are any abrasives in your system) and pressure drop. Check valves can have a lot of pressure drop and high velocities can accelerate erosion along with producing unnecessary noise. I would just use good engineering standards to apply the valves.

Regards checman

 

[kenvlach]

My guess is that the pipe is sized for future increase in capacity. Go with the 2 " valve; whenever a larger pump is needed, then spend money on an appropriate valve.

 

[pumpkind]

Just remember, if the existing pump is designed for the velocity associated with a 2 " discharge - there shall be no problem for the valve either

 

[devaxrayz]

First of all, i want to thanx for all the reply. Sorry not to follow up quickly.

Flow have been determine which is 325 gpm. Artisi, the piping size choosen is 6" because at lower size (4 or 3 inches) the pressure drop and the velocity is high exceed the piping standard that we use (5 -12 fps).

The problem is the pump supplied by vendor has 2" discharge nozzle. So we need to expand it to 6"

For rated flow the pumps has total developed head much higher than required, so it will easily overcome additional pressure drop from 2" valve.

I'm just not sure about using 2" valves since the line sizing is 6".

Checman: u said u would just use good engineering standards to apply the valves. Could I know the standard for valves??

Is there any judment for valve sizing, (like in control valve and orifice sizing we should know wheter the flow will be choked or not..)?

Thanks all

-Rayz-

 

[TD2K]

325 gpm in a 6" line is about 3.6 ft/sec. I'd expect to see that for the pump suction but for the discharge seems a low velocity.

A 4" line would have a velocity of 8.2 ft/sec which would be more typical in my opinion. However, if the discharge piping is long or there is a possibility of future capacity increases, the 6" could be justified. Over and above the velocity, the decision for selecting a pipe diameter is also affected by the overall pressure drop.

For the 2" pump nozzle, you are looking at 35 ft/sec velocities. I wouldn't definitely NOT even consider 2" check valve and block valves. 3" is still close to 14 ft/sec which is higher than I would typically select. Check that the velocity through the check valve is high enough to ensure the check valve is fully open, Crane's technical paper discusses this.

 

[Artisi]

Your flow figure of 325 GPM for a 2" pump doesn't sound right to me - suggest you check your information.

Naresuan University
Phitsanulok
Thailand